It wasn't always used in a sarcastic tone, but considering how it's changed over time, people do use it in that way.

"In older times, the word 'bully' also had a couple of positive meanings, the only trace of which is left in the expression 'bully for you,' which is still occasionally used in British English - I can't comment on US English. I've mostly heard it used in a derisive or sarcastic way, along the lines of 'Well then, aren't *YOU* the clever one?'"
-Ask.com topic